1. Field of the Invention
The invention relates to a clamping device for a defined clamping of differently sized workpieces including two movable clamping elements, which clamp the workpiece on two oppositely disposed sides, and a device for moving the clamping elements together with means for synchronizing the motion of the clamping elements.
2. Brief Description of the Background of the Invention Including Prior Art
In the context of the present invention, the term "defined tightening or defined clamping" concerns a clamping, where workpieces of different sizes are to be positioned, for example, with their center always at the same position in the course of clamping. This requirement exists in particular with tool machines which process rod links and semi finished products such as bars, tubes, or profiles. The requirement is further and in particular present in the case of centerless peeling machines. Peeling machines of this kind serve, in particular, to produce a so-called bright steel from hot-rolled metallic round stock. The bar-shaped round stock is peeled in this case at its cylindrical periphery by a rotary cutter head. The bar itself is secured axially, against undesired rotation and is led through the center borehole in the cutter head by the peeling machine. The rotating cutter head carries three or more inwardly directed cutters which peel the rod on a helical path. Such peeling machines are employed for wire, bars, and tubes. The peeling machines used at the present time operate with a feed-in apparatus on the feed-in side ahead of the cutter head. This feed-in apparatus includes two roller pairs and a clamping carriage is disposed on the discharge side of the cutter head. This clamping carriage secures the bar against twisting and transfers the bar when the rear end of the bar is being peeled. In addition, such peeling machines include guides immediately ahead of and after the cutter head. These guides center the workpiece and damp the vibrations generated by the peeling process.
Modern peeling machines and rough-turning machines can change the feed-in of the round stock during operation, the rotation speed of the cutter head, and the final dimension.
A peeling machine of the above recited kind is known from the German Patent DE-PS 2,055,888, which operates with an infeed roll apparatus, which is formed as a clamping device, and where its two roller pairs form possibly together with their supports the clamping elements and clamp the bar to be peeled centrically relative to the machine center. In other words, the two rollers of one pair are movable relative to the frame of the clamping device in a radial direction relative to the peeling machine center. A cylinder presses the two rollers against the workpiece. One roller is mechanically connected with the cylinder in this case, and the second roller is connected to the piston of the cylinder. The rollers of one pair are synchronized in their clamping motion. Each roller of a pair is hingedly connected via its roller to the ends of a rocker, pivotably supported at the frame of the clamping device. The two rollers are led and guided with their supports at the frame of the clamping device and they are moved apart and then led together for clamping purposes by a hydraulic cylinder. The rocker transfers no clamping forces in a standard situation. The rocker assures only that the clamping rollers are synchronously moved by the hydraulic cylinder.
It is a disadvantage of this clamping device that the center guiding of the bar to be peeled exhibits a play within the range of the tolerances of the synchronization means and, further, allows vibrations of the bars together with the clamping elements. The play of the unit, comprising the rollers with the clamped bar, can lead to an interference and disturbations of peeling and rough turning efficiency, in particular, after an extensive use of the clamping device.